1. Field of the Invention
The present invention is generally related to industrial chemical production plants and waste water treatment, and is more specifically directed to a novel apparatus configuration and method for using the same to recover raw materials, by-products and product from the dilute process condensate streams of chemical production plants. The recovered materials are recycled for use in the production facilities in such a manner as to avoid any significant energy or other efficiency penalties which could negatively impact the plant's operation and overall effectiveness.
2. Description of the Related Art
Large quantities of industrial waste water are daily produced by chemical production and processing plants within the United States and throughout the world. Often times, this waste water is process condensate consisting of dilute streams of raw materials, byproducts and product remaining unrecovered from processing water and/or steam used in various phases of production. For example, in the production of ammonia, steam exiting the plant after use in stripping operations carries trace amounts of methanol, ammonia, carbon dioxide, alkylamines and the like. Although the materials within these streams could be utilized to form product, due to the dilute nature of the condensate, it is generally more cost efficient to simply consider the water as waste water and dispose of the same as needed.
At one time, the bulk of process condensate and industrial waste water was simply discharged into live streams or municipal sewer systems without treatment. However, in view of the potential environmental damage that could result from the release of chemicals into the water systems, as well as the need to conserve the amount of water used daily in operations, methods have been developed for treating the water to remove any contaminants therefrom and recycle the water back to phases of the plant for reuse.
In the field of ammonia production, for example, it is known to use a relatively low pressure steam stripping apparatus such as a conventional stripping tower to treat the process condensate, wherein steam is utilized to strip the contaminates from the condensate. The contaminated overhead is then vented to the atmosphere while the stripped condensate is reused in the plant as cooling tower water make-up, boiler feed water make-up and the like. Alternatively, the contaminated overhead may be destroyed or decomposed such as by burning. Although these conventional low pressure strippers are useful for this purpose, the amount of contaminants and/or noxious vapors vented to the atmosphere is undesirable. In fact, the type and amount of such emissions is the subject of increasingly stringent regulation by the Environmental Protection Agency (EPA), as well as other state and local officials. It is anticipated that the level of emissions now permitted will be substantially reduced in the future, particularly as to potentially harmful compounds such as ammonia and methanol, and will perhaps eventually be prohibited altogether.
In order to overcome these emission problems, a more recently developed method of treating ammonia plant process condensate utilizes relatively high pressure condensate stripping towers, generally operating at 500 pounds pressure (psi) or more to strip contaminants from the condensate. In this method, the high pressure process steam carries the contaminated stripper overhead back to the plant for use in the primary reformer stage of production. Although return of the contaminates to the ammonia plant avoids undesirable venting of contaminants into the atmosphere, injection of the relatively high pressure stream of overhead into the plant requires that the flow of this high pressure stream into the plant be controlled and that this additional stream be taken into account along with the normal steam flow in setting the steam-to-gas ratio. This has the effect of lowering the front-end pressure of the system, lowering ammonia plant capacity and efficiency as well as complicating process control overall. In addition, the high pressure strippers are relatively very expensive and their use requires the complete replacement of the more conventional low pressure strippers that are presently use3d in many plants throughout the world.
Therefore, it is a primary object of the present invention to provide an apparatus and method of treating chemical plant process condensate, wherein the raw materials, product and byproducts (hereinafter referred to collectively as "contaminants") in the condensate are recovered from the water for reuse in the plant.
It is another object of the present invention to provide an apparatus and method of treating process condensate, wherein contaminants in the condensate can be recovered and returned to the plant without accruing significant efficiency penalties to the plant or requiring plant modification.
It is another object of the present invention to provide an apparatus and method of treating process condensate, wherein a conventional low pressure steam stripping tower may be utilized.
Another object of the present invention is to provide an apparatus and method of treating process condensate, wherein a plant using a conventional low pressure steam stripping tower for condensate treatment can be retro-fitted to enable the concentrating and recycling of recovered contaminants back to the plant.
It is another object of the present invention to provide an apparatus and method of treating process condensate that is relatively efficient and cost effective.
A further object of the present invention is to provide an apparatus and method of treating process condensate wherein contaminant air emissions are effectively eliminated.
Yet another object is to provide an apparatus and method of treating process condensate, wherein a substantial amount of the water in the condensate can be recovered having a reduced contaminant content so as to be suitable for reuse in the plant as boiler feedwater make-up which requires high quality, low conductivity water.
Yet a further object of the present invention is to provide an apparatus and method of treating ammonia and/or methanol plant process condensate meeting the objectives heretofore described.